As a typical sealing ring, an O-ring is known. The O-ring is molded in a ring shape with an elastic material such as rubber, and its section is O-shaped. Depending on a required performance and a use, various sealing rings having sectional shapes different from that of the O-ring are also proposed.
The sealing ring typified by the O-ring is used in places where a sealing function such as air tightness or water tightness is required in various industrial equipments and devices.
Under general use conditions of the sealing ring, it is inevitable that an elastic material composing the sealing ring changes in material property or deteriorates in physical property with the passage of time. The sealing ring having deteriorated in property is exchanged with a new sealing ring. An exchange timing of the sealing ring varies with use conditions such as a load and an environment when using it. Some sealing rings may be used for several years, and other sealing rings must be exchanged in a short period not more than several months.
For example, a sealing ring to be attached to a valve of a semiconductor-producing device and its opening-and-closing cover is used under severe conditions such that: high air tightness is required, a load applied upon using is large, and further, the sealing ring has a possibility of contacting with a plasma gas or a corrosive gas. Under such use environments, it is necessary to detect deterioration of a performance of the sealing ring surely and quickly or to surely exchange the sealing ring before its performance is deteriorated. If the use of the sealing ring with the deteriorated performance is continued, a quality performance of a semiconductor product is damaged to thus deteriorate the product yield.
Conventionally, in order to judge whether or not the sealing ring needs to be exchanged, it is necessary that a device fitted with the sealing ring is decomposed to expose the sealing ring and observe it, or that the sealing ring is fetched out to inspect it by an inspection apparatus.
Patent document 1 below proposes a technology in which an inner signal member of a color different from the surface of the O-ring is embedded in the inside of the O-ring. This patent document states that: if the surface of the O-ring is deteriorated, then the inner signal member is exposed to the surface, so it is possible to judge the deterioration of the O-ring from the difference in color.
[Patent Document 1] JP-A-168348/2002 (Kokai)
As to conventional methods to judge the exchange of the sealing ring or to manage the sealing ring, it is difficult to appropriately judge the exchange or make strict management about individual sealing rings when they are used.
For example, as to the art described in the above patent document 1, unless the O-ring is fetched out from its fitting part to observe its surface, it is not possible to judge the deterioration of the O-ring from whether the inner signal member is exposed or not. In order to fetch out the O-ring from its fitting part, it is necessary as a matter of course that the working of the device including the fitting part is stopped to decompose a peripheral device including the fitting part of the O-ring. If the O-ring is not deteriorated, the reworking of the device will be performed after fitting the O-ring again and reassembling the device. During this time, a time loss is large and a human burden is also heavy.
A method is also carried out in which: there are beforehand collected the data with relation to a degree of progress in a deterioration of a performance and a life duration about the sealing ring in a specific fitting place, and therefrom the exchange timing of the sealing ring is estimated. However, unless there is any past data such that the load and environmental conditions, acting on the sealing ring, conform completely to those of the present sealing ring, it is difficult to accurately estimate the exchanging timing. The progress of the performance deterioration may be different due to an individual difference between the sealing rings.
It has a limitation to estimate a degree of progress in a deterioration of a performance and a life duration about each of the sealing rings by only the data collected in the past.
On the scene using a conventional sealing ring, the sealing ring is exchanged if there has passed a definite period during which it is, from such as past experiences, considered possible to sufficiently maintain the performance of the sealing rings regardless of a usage environment and an individual difference. However, this results in also exchanging the sealing ring having a sufficient sealing function, so this leads to much waste of money. The number of times of the exchanging of the sealing ring increases more than necessary, so that unfavorably the operation rate of the apparatus to which the sealing ring is attached decreases largely.
In order to record a history (e.g. a production period and a use-start period) and other managing information with respect to each sealing ring and exchange a sealing ring to be exchanged on the basis of this managing information, it is necessary to strictly manage each sealing ring and its managing information while making their one-to-one correspondence. This is very troublesome. It is very troublesome to give an identification number to each sealing ring and record it every time the sealing ring is attached or exchanged on the scene using the sealing ring. As to a sealing ring in use incorporated within the equipment and apparatus, it is difficult to check, from the outside, which identification number this sealing ring has.